1. Field of the Invention
The present invention relates to a liquid crystal display element provided by enclosing a liquid crystal between a pair of substrates and a multi-layer liquid crystal display element including such elements.
2. Description of the Related Art
Recently, various enterprises and universities are actively engaged in the development of electronic paper on which an image can be electrically rewritten and which can keep an image displayed thereon even when electric power is not supplied. Display methods used for electronic paper include electrophoretic methods utilizing movement of charged particles in air or a liquid, twist ball methods utilizing rotation of two types of charged particles having different colors, and methods utilizing interference reflection at a liquid crystal layer formed by a selective reflection type liquid crystal having bi-stability. Primary characteristics required for electronic paper are low power consumption, the capability of displaying a memorized state of display without electric power, flexibility.
According to a cholesteric liquid crystal display method utilizing a liquid crystal composition which forms a cholesteric phase (such a composition is called a cholesteric liquid crystal or chiral nematic liquid crystal and will hereinafter be referred to as “cholesteric liquid crystal”), a flexible liquid crystal display element can be formed using resin substrates having transparent electrodes or resin substrates having amorphous silicon. Flexible electronic paper can be fabricated by using such a liquid crystal display element as a display section.
A multi-layer liquid crystal display element capable of full-color display utilizing cholesteric liquid crystals has a structure in which a liquid crystal display element for blue reflecting blue (B) light selectively, a liquid crystal display element for green reflecting green (G) light selectively, and a liquid crystal display element for red reflecting red (R) light selectively are formed one over another in the order listed from the side of the element where a display surface is provided. Each of the B, G, and R liquid crystal display elements has a structure formed by enclosing a liquid crystal between a pair of substrates, i.e., top and bottom substrates.
Known methods of enclosing a liquid crystal between a pair of substrates include the vacuum injection method and one drop filling (ODF) method which are commonly used. According to the vacuum injection method, a peripheral seal member in the form of a frame having a partial discontinuation is applied to the periphery of one substrate, and the substrate is then combined with another substrate to form a liquid crystal cell. Thereafter, a liquid crystal is injected into the gap between the pair of substrates by a vacuum pump system using the discontinuation of the peripheral seal member as a liquid crystal injection port. After liquid crystal injection is finished, the liquid crystal injection port is sealed with an adhesive member to enclose the liquid crystal. A photo-curing bonding member, e.g., an acrylic member is used as the adhesive member for enclosure. Such an adhesive member for enclosure comes into contact with the liquid crystal before it is cured and can therefore contaminate the liquid crystal, which can result in display defects of the liquid crystal display element. For this reason, limited types of materials can be used as the peripheral seal member. For example, a thermo-curing epoxy type adhesive member which may include a solvent in an uncured state is a material that is difficult to use as the peripheral seal member.
When compared to glass substrates, resin substrates having flexibility have lower adhesion to an acrylic adhesive member which can be used for enclosing a liquid crystal. Further, since resin substrates have flexibility, an enclosing portion of a liquid crystal display element using such substrates suffers from breakage starting at an edge of the junction rather than surface breakage at the junction unlike an element having glass substrate. Thus, the strength of the resin substrates is further reduced. When the internal pressure of the liquid crystal display element rises as a result of a change in the volume of the liquid crystal attributable to a temperature change, the enclosing portion of the resin substrates can be broken, which results in the problem of leakage of the liquid crystal from the element.
Patent Document 1: JP-A-2006-313404
Patent Document 2: PCT/JP06/304343